A conventional electrophotography method utilizes photoconductive material using various means to form electrical latent images on a photosensitive matter, developing these latent images with toner, transferring the images to a transfer matter such as a sheet of paper if necessary, and fixing them with a heat source such as heating rollers to form permanent visible images.
The dry developing method is widely used to develop electrostatic charge images in the electrophotography described above. In the dry developing method, a 2-component fine powder developing agent is used which contains a toner prepared by dispersing a coloring agent such as dyes and pigments into a resin and a carrier comprising iron powder or glass beads or a one component fine powder developing agent which uses a magnetic toner prepared by dispersing magnetic substance particles such as magnetite into a toner is used.
In the dry developing method, the toner electrified by friction adheres to electrostatic latent images on photosensitive matter due to electrical attraction, thus forming toner images. The toner images on the photosensitive matter are then transferred to a sheet, and the transferred toner is fixed on the sheet to form permanent visible images.
For the fixing process described above, the so-called heated roller method is widely used in which the toner images on said sheet are pressed onto the surface of the heated roller, which has a toner-separating material formed on its surface, as the sheet goes through. In the heated roller method, a toner resin composition which can be fixed at a lower temperature is desirable so as to improve the cost efficiency, including power consumption, and increase the copying speed.
In order to improve the low temperature fixability, a toner resin composition mainly comprising a vinyl-type copolymer(s) with a lower molecular weight has been proposed. However, although the low temperature fixability of the toners is improved by these methods, there were problems in that a phenomenon in which part of the image forming toner is transferred to the surface of the heated roller during fixation and the toner is then transferred to the next paper sheet and contaminates the images ("the offset phenomenon") tends to occur. Also, the toner tends to aggregate.